Why does when we assign to variable x++ we get an old result. But when we print just x++ we get the new result

Question

1. int x = 3;
2. sout(x++); <- result will be 4
3. int y = x++;
4. sout(y);<- result is 3

So when we process/use x somewhere we will get old result. When just printing x++ we somehow get a new result? (This part is confusing me)